Blended fabrics formed of polyester and cotton have found wide acceptance for fabrics, particularly for clothing. Generally speaking, a "blended" fabric of polyester and cotton is formed by spinning a blended yam from cotton fibers and polyester staple fibers. The blended yams are then woven or knitted into the appropriate fabrics. Each of these materials brings certain advantages and disadvantages to a fabric. Cotton is, of course, formed almost entirely of pure cellulose with a typical length of about one inch, but with variations in length from about a half and inch to over two inches. Mature cotton fibers are characterized by their convolutions so that under a microscope, cotton appears as a twisted ribbon with thickened edges. Cotton is light in weight, absorbs moisture quickly and easily, and has a generally favorable texture ("hand") when woven into fabrics. Cotton lacks, however, certain strength characteristics and elastic memory, and thus garments formed entirely of cotton require regular laundering, pressing, and in many cases starching, between wearings by the ordinary user.
Polyester is strong, light in weight, and has excellent plastic memory characteristics. Polyester is crease-resistant, quick-drying, retains its shape in garments, is abrasion-resistant, and requires minimum care. Because of its synthetic nature, however, polyester has a generally unacceptable appearance (at least for most garment purposes) when initially formed as a filament. Accordingly, polyester filaments require texturizing in some fashion to produce acceptable characteristics of appearance, hand, and comfort in yams and fabrics.
Accordingly, blends of cotton and polyester have found wide-ranging acceptance because of their combination of the desirable characteristics of cotton with those of polyester.
The characteristic advantages of polyester are such, however, that efforts continue to develop polyester filament, yams and fabrics that more closely resemble those of cotton, silk, rayon, or other natural fibers. The use of polyester microfibers is one example of this, with the filaments being of such small diameter that they offer exceptionally good esthetic and hand, while retaining all of the benefits of polyester.
A number of chemical modifications have been carried out on polyester to attempt to obtain the desired properties, but such treatments can produce unwanted or unexpected characteristics in the modified polyester. For example, polyethylene glycol can enhance certain polyester properties such as dye uptake, but can decrease other properties, particularly the melt phase characteristics of the polymer, that make it quite difficult to form into acceptable filaments on a continuous commercial basis. In this regard, it will be understood that polyester filament is made in significantly large amounts around the world, and that if modified polyesters are to gain commercial acceptance, they must be essentially compatible with commercial techniques for melt-spinning, texturing, yam spinning and fabric forming techniques; i.e., weaving and knitting.
Accordingly, a need continues to exist for enhanced polyester compositions that have properties as close as possible to those of cotton and other natural fibers while retaining the advantages of polyester.